A computer program has been developed in order to simulate the secondary fragmentation process during fluidized bed combustion of a population of char particles. The simulation intends to predict the evolution of char particle size distribution during combustion. It is based on two statistical functions, one which accounts for the probability density that a particle of a given size breaks into fragments and the other for the size distribution on the basis of the number of fragments generated by the breaking up of the particle. The parameters involved in the simulation have been obtained by minimizing the difference between theoretical predictions and experimental results. The latter were obtained by image analysis of partially burnt samples of anthracite char (d(0) = 1.98 and 3.50 mm, 750 < T-b < 950 degrees C) and graphite particles (d(0) = 1.98 mm, 850 < T-b < 950 degrees C) in a laboratory-scale fluidized bed reactor (inner diameter 5 mm).